Report a watch error instead of eating it when we can't decode

Clients are required to handle watch events of type ERROR, so instead
of eating the decoding error we should pass it on to the client. Use
NewGenericServerError with isUnexpectedResponse to indicate that we
didn't get the bytes from the server we were expecting. For watch, the
415 error code is roughly correct and we will return an error to the
client that makes debugging a failure in either server watch or client
machinery much easier.

We do not alter the behavior when it appears the response is an EOF
or other disconnection.

Kubernetes-commit: 89620d5667adec6c132b2713b79efb1dd2391723

rest/request.go

@@ -595,7 +595,12 @@ func (r *Request) WatchWithSpecificDecoders(wrapperDecoderFn func(io.ReadCloser)
 		return nil, fmt.Errorf("for request %s, got status: %v", url, resp.StatusCode)
 	}
 	wrapperDecoder := wrapperDecoderFn(resp.Body)
-	return watch.NewStreamWatcher(restclientwatch.NewDecoder(wrapperDecoder, embeddedDecoder)), nil
+	return watch.NewStreamWatcher(
+		restclientwatch.NewDecoder(wrapperDecoder, embeddedDecoder),
+		// use 500 to indicate that the cause of the error is unknown - other error codes
+		// are more specific to HTTP interactions, and set a reason
+		errors.NewClientErrorReporter(http.StatusInternalServerError, r.verb, "ClientWatchDecoding"),
+	), nil
 }
 
 // updateURLMetrics is a convenience function for pushing metrics.